Magnetic plated media and process thereof

ABSTRACT

A process for producing magnetic plated media suitable for use in high-performance disk drives is disclosed. A layer of nickel is first provided on a standard aluminum alloy substrate, by electroless deposition, to improve adhesion of subsequent layers. A layer of nickel phosphorous and a magnetic layer of nickel cobalt are then, in turn, electroplated. The plated media disk is then oxidized below a nickel-magnetizing temperature to provide a protective outer surface. 
     A variation of this process is also disclosed. This time a magnetically-shielding copper layer is electroplated over the first nickel layer. The nickel phosphorous and nickel cobalt layers are then electroplated on as before. The plated media can now be oxidized at a temperature higher than the nickel-magnetizing temperature to speed up the process.

BACKGROUND

This invention relates to the plating of magnetic media, and morespecifically to a process utilizing an electroplating process for thedeposition of a thin magnetic layer.

Most currently available plated media, used as magnetic disks for massstorage in data processing, are produced by totally electrolessprocesses. The main problem with such plated media is that theirperformance is limited by noise problems arising from theelectro-magnetic characteristics of the plated layers. The noiseproblems are created within the magnetic layer by the electrolessprocesses. These processes produce non-uniform layers by forming unevencrystalline structures, by including contaminants in the layer, and byforming occasional plating voids. Each of these plating phenomena willcontribute to noise in high density memory devices. This problem isparticularly acute in high performance applications, where higherstorage densities are required.

A known process to reduce the noise problem utilizes electroplatedmedia. It starts with an heat-treatable alloy, such as the 7075 typeavailable from Alcoa Aluminum, which is then anodized to provide asmooth adhesion surface. A layer of copper is deposited on the anodizedsurface by electroplating and is then polished. A layer of nickel-cobalt(NiCo) is electroplated over the now smooth copper layer and is thenexposed to some temperature for a period of time sufficient to producean oxidation layer. For example it may be exposed to a temperature rangeof 580° to 680° F. for approximately an hour. The main problem with thisprocess is that it depends on a non-standard heat-treatable aluminumalloy substrate that can be easily anodized. Such a substrate, althoughcommercially available, is a non-standard item and is very expensive.

SUMMARY

The present invention solves these and other problems by providing amagnetic plated media disk in which a layer of nickel is first providedon a standard aluminum alloy substrate, by electroless deposition, toimprove the adhesion of subsequent layers. In a first embodiment, alayer of nickel phosphorus and a magnetic layer of nickel-cobalt arethen, in turn, electroplated. The disk is then oxidized below anickel-magnetizing temperature to provide a protective wear surface. Ina second embodiment a magnetically shielding copper layer iselectroplated over the first nickel layer to allow the oxidation of thedisk at a temperature higher than the nickel-magnetizing temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a portion of a disk manufactured by afirst embodiment of the process of the present invention; and

FIG. 2 shows a cross-section of a portion of a disk manufactured by asecond embodiment of the process of the present invention.

DESCRIPTION

Referring now to FIG., 1. there is shown a portion 10 of the aluminumalloy substrate contemplated by the present invention. Preferably, sucha substrate is a standard aluminum alloy, for example type 5086available from Alcoa Aluminum, having the shape of a disk suitable foruse in disk drives of the type used in computer systems for magneticstorage. The surface of substrate 10 is preferably polished to asmoothness within a range of 0.2 to 0.5 microinches (arithmeticaverage).

Standard aluminum alloys do not anodize well, thus they prevent thesatisfactory adhesion of the subsequent layers in the electroplatingprocess. It has been found that a layer 12 of nickel, provided by aconventional electroless deposition forms a reliable adhesion layer.Such conventional electroless deposition process is commerciallyavailable from companies such as McDermid, Enthone, Shipley, etc.

For example, the substrate 10 is plated at a rate of 1.5 microinch perminute at a temperature of 182° to 184° F. in an electroless nickel bathof the following composition:

NiSO₄ *6H₂ O--20 grams per liter

N_(a) H₂ PO*H₂ O--22.5 grams per liter

NaC₂ H₃ O₂ --23 grams per liter

Malic Acid--6.9 grams per liter

Lactic Acid--8.2 grams per liter

SnCl₂ --38 mg per liter Other plating baths may be used, for instanceEnthone EN422 available from Enthone Inc. In general, bath conditionssuch as temperature, nickel concentration and pH control the platingrate. An important requirement is that the plated nickel must not becomemagnetic. The thickness of the adhesion layer 12 is sufficient tocompensate for the asperity, or uneveness, of the surface of the alloysubstrate 10, which is normally due to the presence of impurities.

The nickel plated disk is now polished, and layer 14 ofnickel-phosphorous (NiP) is then deposited by electroplating over thenickel adhesion layer 12. This is achieved by conventionallyelectroplating the nickel coated disk in a nickel-phosphorous bath; forexample, at a temperature of 120° F. using 2 amps at 1.5 to 1.8 volts ina bath of the following composition:

NiSO₄ *6H₂ O--50 grams per liter

Na₂ SO₄ --50 grams per liter

H₂ BO₃ --20 grams per liter

NaH₂ PO₂ *H₂ O--10 grams per liter

Antipit #12-70 oz. per 370 liters

Antipit is a commercially available from M & T Chemicals, Inc. It is ahydrocarbon mixture containing wetting agents and surface enhancingmaterials which inhibit the adhesion of Hydrogen gas bubbles to surfacesduring plating operations. Thus, surface roughness due to pitting doesnot occur. The absence of pitting in the NiP layer contributes to thelow noise characteristics of the product disk.

In this and all the other electroplating steps, the anode is attached toa plating fixture inserted in the disk's central opening. The NiP coateddisk is now rinsed and a magnetic layer 16 formed of nickel-cobalt isnow deposited. Again, this is achieved by conventionally electroplatingthe NiP coated disk in a nickel-cobalt bath; for example, at atemperature of 84° F. using 11 amps at 3.0 to 3.5 volts in a bath of thefollowing composition:

NiSO₄ *6H₂ O--50 grams per liter

NaSO₄ --50 grams per liter

CoSO₄ *7H₂ O--27.5 grams per liter

H₃ BO₃ --12 grams per liter

NaH₂ PO₂ *H₂ O--0.48 grams per liter

Antipit #12-70 oz. per 370 liters

The Ni-Co coated disk is then polished.

The substrate 10 and corresponding deposited layers 12 through 16 arenow heated at a temperature of approximately 520° F. for a period of 2to 12 hours to provide an oxide layer 18. Oxide layer 18 serves as theouter protective layer for the media surface. The oxidation step alsoserves to anneal the plated media to further improve adhesion amonglayers. The electromagnetic characteristics of the plated media, andmore specifically the coercivity, are dependent on several parameters,such as the ratio of nickel to cobalt of the magnetic layer 16, theamount of phosphorus that diffuses into this layer 16, and the thicknessof the magnetic layer. In the preferred embodiment the ratio of nickelto cobalt has been approximately 2:8. Diffusion of the phosphorous hasbeen limited approximately from 1 to 2%. For a thickness of layer 16 offrom 3 to 4 microinches the resulting coercivity is approximately 450 to650 oersteds. Table 1 shows a representative sample of operationalconditions to produce the stated coercive forces in high-density disks.

                                      TABLE 1                                     __________________________________________________________________________            ATOMIC % OXIDE PROCESS                                                                            MAGNETIC                                          COERCIVITY                                                                            PHOSPHORUS                                                                             TEMP.                                                                              TIME  LAYER THICKNESS                                   __________________________________________________________________________    450 oe  0.8      580-600                                                                            1-2 hr.                                                                             3-2 u"                                            650 oe  1.0      620  2-2.5                                                                             hr.                                                                             3.0 u"                                            1200 oe 1.3      620  1-1.75                                                                            hr.                                                                             2.8-3.0 u"                                        __________________________________________________________________________

In the present process it is important that the layers under themagnetic layer 16 do not become magnetic, or the media will not beuseable in standard storage systems.

To prevent the nickel layer 12 from becoming magnetic it is insulatedfrom the magnetic layer 16 by the nickel phosphorous layer 14 which isnonmagnetic provided that the concentration of phosphourous is greaterthan approximately 10.5%. Additionally, nickel becomes magnetic at orabove approximately 530° F., thus the oxidation treatment must notapproach or exceed 530° F.

In a second embodiment of the invention, the process starts with thesame standard aluminum alloy substrate, shown as 20 in FIG. 2, asbefore. Again, a layer 22 of nickel deposited by an electrolessdeposition process is provided as the adhesion layer. This is followedby the deposition of a copper layer 24 by an electroplating process.Since the nickel layer 22 is followed by the magnetically inert copperlayer 24, it need not be as thick as in the first method described,since the asperity of the surface of substrate 20 will be compensatedfor by the composite thickness of these two layers. For example, thethickness of the nickel layer 22 is approximately from 90 to 120microinches, while the thickness fo the copper layer 24 is approximately500 microinches.

The copper is deposited by a conventional electroplating process, forexample, by using a current of 54 amps at 2 volts in a bath of thefollowing composition:

CuSO₄ *5H₂ O--200 grams per liter

H₂ SO₄ --4% by volume

HCL(chloride ion)--30 mg per liter

UBAC--4.0 ml per liter

where UBAC is a produt available from UDYLITE Inc. Its active agents arean organic dye, and certain organic acids of chain-lenght 8 to 13, and acommon wetting agent.

A layer 26 of nickel-phosphourous is now deposited, also byelectroplating as discussed before, over copper layer 24. A magneticlayer 28 of nickel-cobalt is now electroplated over layer 26 and theentire assembly is oxidized at a temperature in the range ofapproximately 580° to 680° F. for about 1 hour, in order to provide aprotective layer 30. The nickel phosphorous layer 26 acts as a shield toprevent the copper from diffusing into the nickel cobalt layer 28 andaffecting its magnetic characteristics.

A higher oxiding temperature is used in this second process in order tospeed up the production of magnetic plated media. The fact that thenickel layer 22 becomes magnetic at such temperature is now notdetrimental, since the copper layer 24 shields the intended magneticlayer 28 from the accidental magnetic layer 22.

The additional advantage of the process of this second embodiment,obtained by using the magnetic shielding copper layer 24, is that aprocess restriction present in the prior art has been eliminated. Theprocess restriction arises because the nickel layer 22 will becomemagnetic, regardless of the optimization of the other parametersdiscussed above, between 2.5 and 4 metal turn-overs, commonly referredto as the X number. A metal turn-over is defined as a depletion andrefurbishment cycle of the plating bath. The second process of thepresent invention produces a plated media disk that can allow nickellayer 22 to become magnetic, so that the plating bath can be used formore turn-overs, and so reducing the overall cost of the process.

This completes the description of the present invention. Somemodification will be apparent to persons skilled in the art withoutdeparting from the spirit and scope of this invention. Accordingly, itis intended that this invention be not limited to the embodimentsdisclosed herein except as defined by the appended claims.

What is claimed is:
 1. A process for producing magnetic plated mediacomprising, in sequence, the steps of:electrolessly plating a layer ofnickel on an aluminum substrate; electroplating a layer ofnickel-phosphorous on said plated substrate; and electroplating a layerof nickel-cobalt on said plated substrate.
 2. The process of claim 1further comprising the step of:oxidizing said plated media at atemperature and for a duration sufficient to provide a protectivecoating.
 3. The process of claim 2 wherein said oxidizing temperature isbelow the nickel-magnetizing temperature.
 4. The process of claim 2further comprising the step of: electroplating a layer of copper afterthe plating of said nickel layer and before the electroplating of saidnickel-phosphorous layer.
 5. The process of claim 4 wherein saidoxidizing temperature is at or above the nickel-magnetizing temperature.